Monitoring the physical formation of earprints: optical and pressure mapping evidence

In earprint identification, the formation of earprints is little understood, particularly the distortion of the ear when it is pressed against a listening surface and the effect on the resulting earprint. This lack of understanding causes widespread suspicion about the validity of earprints as forensic evidence. Yet empirical investigations show that crime scene marks from ears are relatively stable. To study earprint formation in real time we introduce an optical apparatus that highlights the ear contact area when pressed against a surface. We report results from a small number of volunteers using this system to log the ear-printing process as they listened at an instrumented surface. Recordings of force history, pressure distribution and growth of the print mark were made. The optical system has proved successful in gaining new insight into the print formation process. From our observations we conclude that involuntary movement and local pressure redistribution during listening at a surface make print formation a decidedly stochastic process. Evidently the stability of the print mark is a result of accumulating the transfer of body oils and waxes over a listening interval during which the ear suffers widely varying amounts of deformation.